Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (which only declare readOnly/non-destructive/non-open-world), the description discloses polling semantics, the meaning of an errorCode of monthly_limit_reached, and the important billing consequence that addresses come back marked as unknown but are still present in results and unbilled. That is exactly the kind of non-obvious behavioral detail an agent cannot get from structured fields.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the return payload, then the polling instruction, then the edge-case caveat. Every clause — especially the unknown-vs-missing billing clarification — carries information an agent would otherwise get wrong.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description takes on the burden of explaining returns and does so for state, verdict counts, and billing, plus the key error case. It does not describe the shape of the per-verdict counts or how to fetch individual results (a separate sibling exists), leaving a small gap for a read tool of this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single parameter with 100% schema description coverage, so the schema already documents jobId. The description adds no format, sourcing, or retrieval hints for the ID (e.g., where to get it), so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb and resource ("Returns one verification job") and enumerates the returned payload (state, per-verdict counts, billing). Saying "one" implicitly distinguishes it from the list sibling, but no sibling or alternative is named explicitly, so it stops short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

"Poll until state is done" gives concrete lifecycle guidance that tells the agent exactly how to drive this tool to a useful result. It does not state when to prefer list_email_verification_jobs or cancel_email_verification_job instead, so no explicit exclusions or alternatives appear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.